When a mobile station places an emergency call, the network typically routes the call to an emergency call centre such as Public Safety Answering Point (PSAP). When the emergency call ends, the MS typically stays in an emergency callback mode for at least the duration of time known as the emergency callback period. During this time, the Emergency Call Centre may attempt to callback the MS.
Mobile stations that subscribe to caller id may attempt to determine that an incoming call is a callback from an emergency call centre by screening the caller id of incoming calls. However, this may not work if the caller id is not recognized as belonging to an emergency call centre. Furthermore, this will not work if the user of the mobile station has not subscribed to the caller id service, or even having subscribed to the caller id service, if a caller invokes caller id restriction when placing a call to the user during the emergency callback period. In addition, if the user does not subscribe to the call-waiting feature, this may prevent the emergency call centre from reaching the user if the user decides to take a non-emergency voice call. This could also happen at any time outside of emergency callback period.
Consequently, there is a need for a standard mechanism on mobile stations to adequately differentiate between an incoming call from an Emergency Call Centre, and an incoming non-emergency call.